5,683 research outputs found
Delay of Disorder by Diluted Polymers
We study the effect of diluted flexible polymers on a disordered capillary
wave state. The waves are generated at an interface of a dyed water sugar
solution and a low viscous silicon oil. This allows for a quantitative
measurement of the spatio-temporal Fourier spectrum. The primary pattern after
the first bifurcation from the flat interface are squares. With increasing
driving strength we observe a melting of the square pattern. It is replaced by
a weak turbulent cascade. The addition of a small amount of polymers to the
water layer does not affect the critical acceleration but shifts the disorder
transition to higher driving strenghs and the short wave length - high
frequency fluctuations are suppressed
Saturation of Turbulent Drag Reduction in Dilute Polymer Solutions
Drag reduction by polymers in turbulent wall-bounded flows exhibits universal
and non-universal aspects. The universal maximal mean velocity profile was
explained in a recent theory. The saturation of this profile and the crossover
back to the Newtonian plug are non-universal, depending on Reynolds number Re,
concentration of polymer and the degree of polymerization . We
explain the mechanism of saturation stemming from the finiteness of
extensibility of the polymers, predict its dependence on and in the
limit of small and large Re, and present the excellent comparison of our
predictions to experiments on drag reduction by DNA.Comment: 4 pages, 4 figs., included, PRL, submitte
Cold ideal equation of state for strongly magnetized neutron-star matter: effects on muon production and pion condensationn
Neutron stars with very strong surface magnetic fields have been suggested as
the site for the origin of observed soft gamma repeaters (SGRs). In this paper
we investigate the influence of such strong magnetic fields on the properties
and internal structure of these magnetized neutron stars (magnetars). We study
properties of a degenerate equilibrium ideal neutron-proton-electron (npe) gas
with and without the effects of the anomalous nucleon magnetic moments in a
magnetic field. The presence of a sufficiently strong magnetic field changes
the ratio of protons to neutrons as well as the neutron drip density. We also
study the appearance of muons as well as pion condensation in strong magnetic
fields. We discuss the possibility that boson condensation in the interior of
magnetars might be a source of SGRs.Comment: 10 pages included 9 figures, ApJ in pres
Possibility of the new type phase transition
The scalar field theory and the scalar electrodynamics quantized in the flat
gap are considered. The dynamical effects arising due to the boundary presence
with two types of boundary conditions (BC) satisfied by scalar fields are
studied. It is shown that while the Neumann BC lead to the usual scalar field
mass generation, the Dirichlet BC give rise to the dynamical mechanism of
spontaneous symmetry breaking. Due to the later, there arises the possibility
of the new type phase transition from the normal to spontaneously broken phase.
The decreasing in the characteristic size of the quantization region (the gap
size here) and increasing in the temperature compete with each other, tending
to transport the system in the spontaneously broken and in the normal phase,
respectively. The system evolves with a combined parameter, simultaneously
reflecting the change in temperature and in the size. As a result, at the
critical value of this parameter there occurs the phase transition from the
normal phase to the spontaneously broken one. In particular, the usual massless
scalar electrodynamics transforms to the Higgs model
Nonlinear Diffusion Through Large Complex Networks Containing Regular Subgraphs
Transport through generalized trees is considered. Trees contain the simple
nodes and supernodes, either well-structured regular subgraphs or those with
many triangles. We observe a superdiffusion for the highly connected nodes
while it is Brownian for the rest of the nodes. Transport within a supernode is
affected by the finite size effects vanishing as For the even
dimensions of space, , the finite size effects break down the
perturbation theory at small scales and can be regularized by using the
heat-kernel expansion.Comment: 21 pages, 2 figures include
Hot Gauge Theories and Phases
In this paper the several aspects of the symmetry in gauge theories
at high temperatures are discussed. The metastable bubbles in the
gauge theories with fermions may have, generically, unacceptable
thermodynamic behavior. Their free energy with a positive
proportionality constant. This leads not only to negative pressure but also to
negative specific heat and, more seriously, to negative entropy. We argue that
although such domains are important in the Euclidean theory, they cannot be
interpreted as physical domains in Minkowski space. The related problem is
connected with the analysis of the high-temperature limit of the confining
phase. Using the two-dimensional QCD with adjoint fermions as a toy model we
shall demonstrate that in the light fermion limit in this theory there is no
breaking of the symmetry in the high-temperature limit and thus there
are no bubbles.Comment: preprint PUPT-1415, 21
Colloquium: Theory of Drag Reduction by Polymers in Wall Bounded Turbulence
The flow of fluids in channels, pipes or ducts, as in any other wall-bounded
flow (like water along the hulls of ships or air on airplanes) is hindered by a
drag, which increases many-folds when the fluid flow turns from laminar to
turbulent. A major technological problem is how to reduce this drag in order to
minimize the expense of transporting fluids like oil in pipelines, or to move
ships in the ocean. It was discovered in the mid-twentieth century that minute
concentrations of polymers can reduce the drag in turbulent flows by up to 80%.
While experimental knowledge had accumulated over the years, the fundamental
theory of drag reduction by polymers remained elusive for a long time, with
arguments raging whether this is a "skin" or a "bulk" effect. In this
colloquium review we first summarize the phenomenology of drag reduction by
polymers, stressing both its universal and non-universal aspects, and then
proceed to review a recent theory that provides a quantitative explanation of
all the known phenomenology. We treat both flexible and rod-like polymers,
explaining the existence of universal properties like the Maximum Drag
Reduction (MDR) asymptote, as well as non-universal cross-over phenomena that
depend on the Reynolds number, on the nature of the polymer and on its
concentration. Finally we also discuss other agents for drag reduction with a
stress on the important example of bubbles.Comment: Invited Colloquium Paper for Reviews of Modern Physics, 24 pages, 18
Figs., submitte
Получение фталатзамещенного вторичного полиэтилентерефталата и изучение его изотермической кристаллизации
Objects. Due to the polymer waste accumulation, the search for new directions for their utilization is urgent. Chemical recycling methods are of considerable interest, which allow one to obtain the original monomers or change the compositions of the copolymers. From the point of view of building a circular economy, a promising material is polyethylene terephthalate (PET), on the basis of which amorphous copolyesters can be obtained. The study aimed to analyze the simultaneous glycolysis and interchain exchange reactions of PET in the presence of the oligoethylene phthalate modifier with hydroxyl end groups and the study of isothermal crystallization of poly(ethylene phthalate-co-terephthalates) with different phthalate contents obtained in this way.Methods. Oligoethylene phthalate is synthesized by polycondensation. Poly(ethylene phthalateco-terephthalates) were obtained by the interaction of post-consumer PET with oligoethylene phthalate. The composition of the oligomer and copolymers was confirmed using Fourier-transform infrared spectroscopy, thermal characteristics and crystallization half-times were determined by differential scanning calorimetry.Results. In this work, the use of the post-consumer PET chemical recycling process, aimed at obtaining copolyesters under the influence of small modifier amounts was proposed. The process consisted in carrying out the combined interchain exchange and degradation with a complex oligoester different from PET. Poly(ethylene phthalate-co-terephthalate) copolymers were obtained via reaction of post-consumer poly(ethylene terephthalate) flakes and synthesized oligoethylene phthalate resin in the melt phase in the absence of catalyst. The effect of phthalate concentration in polymer on the isothermal crystallization of phthalate substituted poly(ethylene terephthalate) was estimated.Conclusions. The hypothesis about the possibility of using an oligoester modifier to obtain the PET-based copolymer at the high rate and without reducing the molecular weight to values characteristic of a monomer or oligomer has been confirmed. The process can be used to obtain random copolyesters based on post-consumer PET. The phthalate unit concentration increase is followed by decrease in the glass transition temperature, temperature and heat of fusion, and increase in crystallization half-times. Phthalate has a better ability to retard PET crystallization than 2-methyl-1,3-propanediol or furandicarboxylic acid, but is inferior to some of the other modifiers known.Цели. Накопление полимерных отходов в последнее время обуславливает поиск новых подходов к их утилизации. Значительный интерес представляют химические способы вторичной переработки, которые позволяют получить исходные мономеры или изменить составы сополимеров. С точки зрения построения экономики замкнутого цикла перспективным материалом является полиэтилентерефталат (ПЭТ), из которого в процессе химического рециклинга получают аморфные сополиэфиры. Работа посвящена исследованию одновременного протекания реакций гликолиза и межцепного обмена ПЭТ в присутствии модификатора олигоэтиленфталата с гидроксильными концевыми группами и изучению изотермической кристаллизации поли(этилен фталат-со-терефталатов) с разным содержанием фталата, полученных таким способом.Методы. Олигоэтиленфталат синтезирован поликонденсацией. Поли(этилен фталат-со-терефталаты) получены взаимодействием вторичного ПЭТ с олигоэтиленфталатом. Состав олигомера и сополимеров был подтвержден с использованием ИК-Фурье спектроскопии, термические характеристики и полупериоды кристаллизации определяли методом дифференциальной сканирующей калориметрии.Результаты. Разработан процесс получения сополиэфиров, основанный на химическом рециклинге вторичного ПЭТ под действием малых количеств модификатора. Отличительной особенностью процесса является одновременное протекание реакций межцепного обмена и деструкции сложным олигоэфиром, отличным по природе от ПЭТ. Реакцией в расплаве вторичного ПЭТ и синтезированного олигоэтиленфталата в отсутствие катализатора были получены поли(этилен фталат-со-терефталаты). Изучено влияние концентрации фталата в полимере на температуру стеклования, температуру и теплоту плавления, изотермическую кристаллизацию фталатзамещенного ПЭТ.Выводы. Подтверждена гипотеза о возможности использовани олигоэфирного модификатора для получения сополимера на основе ПЭТ с высокой скоростью и без снижения молекулярной массы до значений, характерных для мономера или олигомера. Процесс может быть использован для получения статистических сополиэфиров на основе вторичного ПЭТ. С увеличением концентрации звеньев фталата происходит снижение температуры стеклования, температуры и теплоты плавления, увеличение полупериодов кристаллизации. Фталат обладает лучшей способностью замедлять кристаллизацию ПЭТ, чем 2-метил-1,3-пропандиол или фурандикарбоновая кислота, но уступает некоторым другим известным модификаторам
Chronology Protection in Generalized Godel Spacetime
The effective action of a free scalar field propagating in the generalized
Godel spacetime is evaluated by the zeta-function regularization method. From
the result we show that the renormalized stress energy tensor may be divergent
at the chronology horizon. This gives a support to the chronology protection
conjecture.Comment: Latex 6 pages, typos correcte
Massive scalar field in multiply connected flat spacetimes
The vacuum expectation value of the stress-energy tensor is calculated in several multiply
connected flat spacetimes for a massive scalar field with arbitrary curvature
coupling. We find that a nonzero field mass always decreases the magnitude of
the energy density in chronology-respecting manifolds such as ,
, , the M\"{o}bius strip, and the Klein bottle.
In Grant space, which contains nonchronal regions, whether diverges on a chronology horizon or
not depends on the field mass. For a sufficiently large mass remains finite, and the metric
backreaction caused by a massive quantized field may not be large enough to
significantly change the Grant space geometry.Comment: 19 pages, REVTeX, 5 figures in separate uuencoded compressed fil
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